Research projects within the Centre's remit

 

Project portfolio

The Centre would manage a portfolio of research projects within the identified key technology areas. A speculative list of representative projects is given here.

  1. System Configuration Modelling

    2. Various system configurations are easily conceived - for example the receiver could be surface-based or in Earth orbit. Similarly, different laser wavelengths have various advantages and disadvantages, both for transmission and reception, and for their scattering and absorption characteristics within the atmosphere. Detailed models will be needed to assess such major system parameters. Differing technologies will be applicable to different approaches, and it is likely that no one solution will be a clear favourite until more research is undertaken in the key technologies.
  2. Computer Simulation

    3. Computer simulation of a Mars link based on photon counting detectors. The simulation would work by putting a sequence of bits through a simulated link modeling the photon noise from signal and background, and dark count. The model would include the modulation and demodulation process (PPM), and Forward error correction codes (e.g. Convolutional, Reed Solomon) and the dead time set by the detectors. The output of the simulation would be compared with the original bit sequence to determine the bit error rate (BER) as a function of various parameters. Such modeling is needed to give a clearer idea of the performance of such a link in terms of photons per bit, and data rates; to determine the effect of background and dark count on performance; to determine the number of photon counters needed to support a given data rate; and to determine the most effective error correction schemes.
  3. Laser transmitter development

    4. Much work needs to be done to realise a laser technology with suitable characteristics. The high power, high beam quality problem has been solved for certain specific lasers, e.g. for LIGO by the University of Adelaide. This work needs to be extended to other possible wavelengths, to maximise the efficiency of the lasers for space-based operation, and to allow scalable communications-suitable technology, possibly with multiple frequencies carrying parallel data.
  4. Daylight Sky Brightness Monitoring

    5. Reducing the background to a minimal level is essential to getting photon noise limited performance in daylight. We will most easily get sky brightness data in a useful form if we measure it ourselves. A relatively simple system could be set up using a small automated telescope (such as a Celestron or Meade amateur telecope) controlled by a PC, with a filter wheel and visible and IR photodiode detectors. This could easily be programmed to make a set of measurements of the wavelength and position dependence of sky brightness. A monitoring program needs to be carried out over a sufficent period to determine the full range of varaibility. Considerable variations can be expected depending on the quantity of scattering particles in the atmosphere.
  5. Daytime Seeing Monitoring

    6. The other important factor determining the background level is the aperture size and this is determined by the daytime seeing. NASA studies have suggested that daytime seeing is 5 to 10 times worse than nighttime seeing (of 1 to 2 arcsec), and so a 20 arcsec aperture is needed. This seems rather pessimistic. We need to look at what has already been done on daytime seeing (e.g. by solar astronomers), but again it may be useful to start our own monitoring program to get a good set of statistics. The AAO can measure daytime seeing with the AAT and its acquisition camera on bright stars. Alternatively an instrument could be built specifically for daytime seeing measurements (e.g. an IR DIMM) though this would be a more expensive approach.
  6. Tunable Filter Selection

    7. To cope with the background levels we will need very narrow band filtering to isolate the laser wavelength. The results of steps 1,2 and 3 will enable the requirement to be fully specified but it is likely that we will need filters narrower than 10-5 and tunable over a small range to allow for the spacecraft velocity. We need to determine the most approporiate filter technology.
  7. Design Study for the Multi-Telescope Telescope

    8. Develop the optical and mechanical design for a multi telescope system along the lines Peter Gillingham has suggested. Initially we would aim at a prototype system using say 4 1m or smaller telescopes. However, the design would need to be scalable to a final system of about 10m effective aperture composed of 2m telescope tube assemblies.
    The prototype telescope could perhaps make use of a standard telescope mounting and control system from EOS, with just the tube assembly being non standard.
  8. Laboratory Demonstration of a Photon Counting Data Link

    9. This step would demonstrate a working data link in the laboratory, operating at photon rates of a few photons per bit, and would enable us to test the performance figures determined by the computer simulation. The transmitter could use a standard fibre-optic communication light source. It could use hardware error correction coding, and a PPM modulator which we may have to build. The receiver would use a small number of Silicon APD photon counters (commercially available modules, e.g. from Perkin Elmer). We would have to develop the high speed electronics to perform the photon timing, and software for demodulation and decoding which has to be able to handle high data rates (though for initial testing the data processing may not have to keep up with the data if sufficient buffering memory is available). The software development could build on that already used in step 1.
  9. Prototype Telescope

    10. Build a prototype telescope on the basis of the outcomes of the earlier modelling work and design study.
  10. Detector System

    11. Build a detector system for the prototype telescope based on experience from the laboratory system demonstrated previously.
  11. Tunable Filter System

    12. Build a tunable filter system (one filter for each sub-telescope, or perhaps one for each detector) based on results of the research into sky brightness and wavelength selection criteria.
  12. Integrate Prototype Telescope System

    13. Integrate the telescope with its detector system and tunable filter system, autoguiding system etc.
  13. Telescope Tests

    14. Various tests not involving data transmission. For example test ability to work close to the Sun in daylight without excessive background. Test ability to track and guide on a moving satellite.
  14. Ground Communication Tests

    15. This is probably most easily done if the telescope is designed allowing it to point horizontally, for ground-to-ground communications testing. The transmitter need only be low power, similar to that used for the laboratory tests.
  15. Ground-Space-Ground Communication Tests

    16. This would use a laser transmitter on the ground and bounce a signal off a laser ranging satellite to return a weak signal to the receiver. This sort of test should test pretty well all aspects of the system. For example, the ability to track a moving object, to operate in daylight and to communicate at low signal levels.
  • Further Development
    • The next step would be to demonstrate Space-Ground communication from Earth orbit. This would involve a transmitter in orbit. To accurately simulate the Mars communication link, this transmitter would have much lower power and a wider beam than the proposed Mars transmitter. It is likely that such a test would be beyond the initial five-year ARC funding of the Centre, and would certainly require substantial collaboration with NASA, but it is hoped that further funding sources will allow the Centre to continue its research.
    From there we would move on to developing a full scale prototype receiving telescope and demonstrating deep space communication to Earth.

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Originally created by Andrew McGrath on July 10, 2002